Conventional aircraft collision avoidance systems which have heretofore been used or studied in general relate essentially to such a type of system wherein ATC transponder response signal of another aircraft responding to such interrogation signal delivered from the collision avoidance system of a subject aircraft is received to catch approximate position of the other aircraft from a period of time required for such interrogation and response, electric field intensity received, bearing the the like, and these results are indicated on an indicator. In this system, it is general that such circle corresponding to a required radius, e.g., 2 n.m. (nautical mile) centering around the subject aircraft is described on the indicator in order to concentrate pilot's attention to the other aircraft with actually threatening of collision viewed from the subject aircraft, and only the other aircraft positioned within the circle are judged as threatening aircraft to indicate them on the indicator.
In this type of conventional indicating system, however, the circle displaying said warning airspace is fixed to, for example, a radius of about 2 n.m., so that there is such disadvantage that sufficient effect cannot be attained dependent upon speeds of the subject and other aircraft.
Specifically, if it is assumed that the subject and another aircraft are approaching with a head to head relationship at each velocity of 500 kt (knots), a period of time from the point when said other aircraft appears in said circle to the point when both the aircraft collide with each other is t=2/(500+500) hours=7.2 seconds. This is absolutely insufficient for avoiding operation of the collision. For the sake of such collision avoidance, when a radius of the circle displaying said warning airspace is increased, number of the aircraft displayed in the circle increases. This bothers extremely pilot so that it is self-evident to be difficult for the pilot that his attention is concentrated to the true threatening aircraft, and hence such system has been difficult for practical application.
On one hand, in the case where the ATC transponder mounted on said other aircraft is one being capable of responding to interrogation signal in mode C or S, the response signal contains altitude information of the very other aircraft, so that it is possible to detect an altitude different between the subject and other aircraft. In this case, it is usual to indicate each altitude difference of other aircraft flying around the subject aircraft with respect thereto.
However, in conventional indicating systems for threatening aircraft as mentioned above, manner of the indication is complicated, besides most of them display merely an altitude difference between the subject and other aircraft irrespective of attitudes of them, e.g., ascending or descending attitude and the like, so that these systems involve such disadvantage by which not so effective results are obtained for collision avoidance.
Furthermore, there have heretofore been proposed a variety of systems in which existence or positions of approaching aircraft, and in its turn change in relative positions of a subject and other aircraft with time are indicated for pilots of aircraft in order to prevent aircraft collision accident from occurring.
Among these systems, there is a manner for indicating change in relative positions between the subject and other aircraft with time, i.e., tracking display for the pilots.
In order to precisely track the courses of other aircraft, however, it is necessary that relative distances and bearings of the subject to other aircraft, besides altitudes of them are detected from response signals of the ATC transponders mounted on the other aircraft flying around the surroundings of the subject aircraft, the information detected is stored in a memory, change of these amounts detected with time is calculated, and such results are momentarily indicated in indicator. Thus, such system requires memory having large capacity, and it cannot be avoided that software to be used for operation becomes complicated and enormous, so that there is such disadvantage that aircraft collision avoidance systems to be mounted on the respective aircraft become large-sized and expensive.
Accordingly, the present invention has been made to eliminate disadvantages involved in conventional indicating systems for warning airspace or threatening aircraft in aircraft collision avoidance system as described above. It is an object of the present invention to provide an indicating system for warning airspace or threatening aircraft in aircraft collision avoidance system wherein a shape of the warning airspace is transformed into a required one in response to the speed of a subject aircraft, whereby a time necessary for avoiding operation of collision of the subject and other aircraft is maintained and at the same time, diversion of pilot's attention with respect to its true threatening aircraft is prevented to attain safety in airline service, besides indication of threatening aircraft is decided and made in relation to attitude of the subject aircraft, whereby the system itself is made simple and inexpensive, and further pilot's judgement required for operation of collision avoidance is made easy. Another object of the present invention is to provide an indicating system for warning airspace or threatening aircraft in aircraft collision avoidance system wherein detected data of other aircraft's distances and bearings are displayed with a required afterglow time, whereby courses of the other aircraft may simply and inexpensively be indicated.